Zero-invasion acidic drilling fluid

ABSTRACT

A drilling fluid system using retarded acid systems such as gelled acid (VES or polymer) and/or emulsified acid to drill carbonate formations (calcite and dolomite). Foamed acid may be used in low abnormal pressure carbonate reservoirs. The drilling fluid system permits drilling a target hydrocarbon-producing formation with zero-invasion of the drilling fluid system. A method for using the drilling fluid system for fluid loss control during drilling operations.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to an acidic drilling fluid system,wherein the system comprises an aqueous acidic solution, a silicate, anda hydro-carbon based isolation fluid, and wherein the system targets ahydrocarbon producing formation with zero invasion. The inventionfurther includes a method of forming a zero-invasion seal on the face ofa well bore using the acidic drilling fluid system.

2. Description of the Related Art

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly or impliedly admitted as prior art against the presentinvention.

The design of drilling fluid typically includes several additives thatare compatible with reservoir fluids and a spectrum of accurately sizedsolids that can prevent filtration but still provide a thin cake. It isa common practice to enhance the properties of the drilling fluid tocontrol the stability of oil and gas wells as well as to handle itsregular function of the drilling fluid. Several ways exist to selectdrilling fluid additives and their design depends on the way thedrilling fluids are executed or the fluid used therein. When thesefluids are pumped at pressures higher than the formation pore pressure,the operation is referred to as an overbalance drilling operations. Inoverbalance drilling operations, one of the drilling fluid's basicfunctions is to exert hydrostatic pressure over the permeable formationto prevent kicks since the drilling fluid pressure is normally keptabove the formation pore pressure. The positive pressure differentialbetween the drilling fluid and formation pore pressure causes thedrilling fluid to invade the permeable formation hence the suspendedsolids in the mud are deposited on the face of the permeable formationto build a filter cake over the formation face, decreasing the rate offiltrate invasion. In addition to the deposition of drilling mudparticles on the formation face around the wellbore, the small particlesin the mud invade the formation causing damage surrounding the wellbore.Normally, the depth of particles invasion depends on the filter cakepermeability, drilling fluid design, and pore size.

Filter cake or mud cake is used conventionally during drillingoperations to prevent fluid losses to the formation and to allow goodcirculation of drilling fluids and suspended cuttings to the surface forremoval from the well. Formation of an effective filter cake depends ona very well designed drilling system including mud fluids and additives.The drilling fluid is normally designed for minimum infiltration andsolid invasion into the formation. On one hand, the filter cake mustwithstand high differential overbalance pressures. On the other hand,reduced oil and gas production can result from reservoir damage when apoor filter cake allows deep filtrate invasion. The drilling mud systemsundergo comprehensive testing procedures to determine infiltration rateand filter cake properties such as thickness, toughness, slickness andpermeability.

Typically, the cuttings formed as a drill removes portions of aformation separate from the drilling mud and are removed usingcontaminant removal equipment. The effect of introducing formationcutting particles, if not separated, to the drilling fluid during thedrilling operation is significant from the point of view of the filtercake's properties. The presence of particles will degrade theperformance of the drilling fluid as well as increase the filter cakethickness and permeability. Therefore, forming an effective thinimpermeable filter cake still one on the most hard and a challengingtasks of drilling operations.

For long horizontal well sections the filter cake's properties are notconstant, heterogeneity effects are often more severe in horizontalwells than in vertical wells because of axial variation of the depth ofthe damage surrounding the wellbore. This is also significant difficultythat must be overcome in order to improve drilling operations. Althoughseveral methods may be employed to overcome this challenge, e.g., use ofa smart drilling fluid, there is no existing technique that enablespumping the drilling fluids with good diversion of the fluids.Generally, when a long horizontal formation is drilled, the drillingfluids tend to get deeper invasion in more highly permeable parts of thewell. Therefore, the zone with high permeability receives heavy fluidand particle invasion whereas the parts with low permeability receiveless damage. On the other hand, in homogeneous formations, especiallyfor long laterals, fluid tends to invade deeper in the heel of the welldue to the long time the heel is exposed to drilling. Less invasionoccurs in parts of the well away from the heel, e.g., the “toe”.

A method and drilling fluid system that can be used to generate quick,thin, uniform and impermeable filter cake layer in horizontal andvertical wells has so far not been available. Moreover, there is a needfor improved drilling system compositions and methods of using drillingfluid system that result in zero invasion into a well formation, do notdamage the formation, and form a sealing layer only on the face of theformation.

BRIEF SUMMARY OF THE INVENTION

The foregoing paragraphs have been provided by way of generalintroduction, and are not intended to limit the scope of the followingclaims. The described embodiments, together with further advantages,will be best understood by reference to the following detaileddescription taken in conjunction with the accompanying drawings. Oneembodiment of the disclosure includes an acidic drilling fluid system.

In another embodiment the acidic drilling fluid system comprises anaqueous acidic solution, a silicate, and a hydrocarbon-based isolationfluid.

In another embodiment the aqueous acidic solution, the silicate and thehydrocarbon-based isolation fluid are in the form of an emulsion.

In another embodiment the emulsion is capable of being broken by contactwith a surface of a well bore in a hydrocarbon producing formation.

In another embodiment the broken emulsion initiates interaction betweenthe aqueous acidic solution and the silicate to form a gel.

In another embodiment the gel creates an impermeable filter cake layerthat seals the face of the formation where the gel contacts theformation.

In another embodiment the infiltration volume of the drilling systeminto the formation during drilling operations is zero.

In another embodiment the aqueous acidic solution is a gelled acidcomprising HCl.

In another embodiment the hydrocarbon-based isolation fluid is anemulsified diesel fluid.

In another embodiment the drilling system is used in a method fordrilling a well into a hydrocarbon producing formation withzero-invasion.

In another embodiment the aqueous acidic solution and the silicate aredelayed from interacting with one another until the emulsion is broken.

In another embodiment the silicate and the aqueous acidic solution forma gel. In another embodiment the filter layer cake is created in anamount effective to overcome exerted pressure during pumping of thedrilling fluid.

In another embodiment the acidic drilling fluid system forms a sealinglayer only on the face of the formation.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 illustrates a high pressure and high temperature filter pressfluid loss test apparatus that tests the drilling fluid system;

FIG. 2 is a graph that determines the acid amount weight percentagebased on the mineralogy of the drilled formation; and

FIG. 3 is a graph that shows the determination of the adequate quantityof silicate weight percentage to generate an effective filter cake overthe face of the permeable formation based on the permeability range.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views.

One embodiment of the disclosure includes a drilling fluid systemcomprising an aqueous acidic solution, a silicate, and ahydrocarbon-based isolation fluid, polymer, or viscoelastic surfactant(VES). The aqueous acidic solution may comprise any acid including butnot limited to HCl, HBr, HI, HF, H₂SO₄, or HClO₄. Organic acids such asformic acid, acetic acid and priopionic acid may also be used, alone orin combination with one or more inorganic acids.

In one embodiment the viscoelastic surfactant is comprised of an aqueousmedium, an effective amount of an inorganic water soluble salt, and aneffective amount of at least one surfactant selected from the groupconsisting of an anionic surfactant, a nonionic surfactant, and ahydrotropic surfactant and one or more hydrophobic organic alcohol. Theanionic surfactant may be selected from compounds including but notlimited to alkyl sulfates, alkyl ether sulfates, alkyl ester sulfonates,alpha olefin sulfonates, linear alkyl benzene sulfonates, branched alkylbenzene sulfonates, linear dodecylbenzene sulfonates, brancheddodecylbenzene sulfonates, alkyl benzene sulfonic acids, dodecylbenzenesulfonic acid, sulfosuccinates, sulfated alcohols, ethoxylated sulfatedalcohols, alcohol sulfonates, ethoxylated and propoxylated alcoholsulfonates, alcohol ether sulfates, ethoxylated alcohol ether sulfates,propoxylated alcohol sulfonates, sulfated nonyl phenols, ethoxylated andpropoxylated sulfated nonyl phenols, sulfated octyl phenols, ethoxylatedand propoxylated sulfated octyl phenols, sulfated dodecyl phenols,ethoxylated or propoxylated sulfated dodecyl phenols. The anionicsurfactant may be selected from compounds including but not limited toalkyl sulfates and alpha olefin sulfates, dodecylbenzene sulfonic acid,linear and branched alkyl benzene sulfonates, dodecylbenzene sulfonicacid, and linear and branched alkyl benzene sulfonates. The nonionicsurfactant is selected from compounds including but not limited toethoxylated octyl phenols, polypropylene glycols, ethoxylated linearalcohols, and ethoxylated nonyl phenols. The hydrotropic surfactant isselected from compounds including but not limited to dicarboxylic acids,phosphate esters, sodium xylene sulfonate, and sodium dodecyl diphenylether disulfonate. The hydrophobic organic alcohol is selected fromcompounds including but not limited to ethanol, diethanol, and propanolalcohol ethers, ethylbenzyl alcohol, 2-propanol, 2-ethyl-1-hexanol,1-octanol, and 2-octanol, and mixtures thereof.

A polymer may be used together or separately from the viscoelasticsurfactant. Examples of polymers that may be used in the drilling fluidsystem include polyacrylamide, partially hydrolyzed polyacrylamide,polyurethane, polybutylene and other polyalpha-olefins, and polyvinylchloride.

The use of viscoelastic surfactants and/or polymers may impartproperties to the drilling fluid system such as an increase in strain onapplication of constant stress; decreased stress on application ofconstant strain (e.g., the drilling fluid system may exhibit relaxing orsagging); cyclic loading may function to dissipate mechanical energy;frictional resistance can occur if the drilling fluid system is cycled.The inclusion of a viscoelastic surfactant and/or polymer provides aviscous material that can undergo changes in strength or resistanceunder load.

The hydrocarbon-based isolation fluid is preferably diesel fuel. Thediesel fuel may be any of fractional distillate of petroleum, fuel oil,biodiesel, biomass to liquid (BTL) fuel or gas to liquid (GTL) diesel.The diesel may be produced from the fractional distillation of crude oilat temperatures between 200° C. and 350° C. The hydrocarbon materialspreferably represent a mixture of hydrocarbons having between 8 and 21carbon atoms per molecule although small amounts of higher carbon numbermaterials may be present. Other hydrocarbons such as more highlypurified petroleum distillates may be used.

In one embodiment the drilling fluid system comprises a gelled acid. Thegelled acid may comprise 10% acid and 90% gel, 20% acid and 80% gel, 30%acid and 70% gel, 40% acid and 60% gel, 50% acid and 50% gel, 90% acidand 10% gel, 80% acid and 20% gel, 70% acid and 30% gel, or 60% acid and40% gel. The gelled acid may be a visceoelastic surfactant based geland/or a polymer based gel. The gelled acid comprises HCl or any otheracid including but not limited to HBr, HI, or HF, or the acid that mayotherwise be in the aqueous acidic solution. Preferably about 15% gelledacid is used in the drilling fluid system.

In another embodiment the drilling fluid system comprises an emulsifiedacid. The emulsified acid may be a diesel based solution although theorganic portion of the emulsion may be any hydrocarbon based fluidincluding other petroleum derived distillates. The emulsified acid maycomprise 10% acid and 90% diesel, 20% acid and 80% diesel, 30% acid and70% diesel, 40% acid and 60% diesel, 50% acid and 50% diesel, 90% acidand 10% diesel, 80% acid and 20% diesel, 70% acid and 30% diesel, or 60%acid and 40% diesel. The emulsified acid is used to drill carbonateformations such as calcite and dolomite. Preferably about 15% emulsifiedacid is used in the drilling fluid system.

In another embodiment foamed acid may be used in low abnormal pressurecarbonate reservoirs in place of gelled acid or emulsified acid. Inanother embodiment the foamed acid comprises an aqueous based fluid, aninert gas, and a blend of at least one alkyltrimethylammmonium chlorideand an amine oxide selected from the group consisting ofbis(2-hydroxyetyl) cocoamine oxide, dimethylhexadecylamine oxide, anddimethyl-hydrogenated tallowamine oxide. Preferably the onealkyltrimethylammmonium chloride is cocotrimethyl ammonium chloride.Preferably the amine oxide is bis(2-hydroxyethyl) cocoamine oxide. Theblend is preferably present in an amount effective to impart foamingproperties to the aqueous based fluid. Preferably the aqueous basedfluid is a brine composition.

In other embodiments the foamed acid is an organic or inorganic acidthat is foamed with a foaming agent such as carbon dioxide or an inertgas, preferably carbon dioxide. Inorganic acids include H₂SO₃, HCl, HI,HBr, HF, HNO₃, H₂C₂O₄, H₃PO₄, H₃PO₂, HIO₄, H₂CO₃, H₂SiF₆, HMnO₄, H₂SO₄,HClO₄, HClO, H₂CO₃, H₃BO₃, and H₂Cr₂O₇. Organic acids include CitricAcid, Formic Acid, Malonic Acid, Tartartic Acid, Glutamic Acid, PhthalicAcid, Azelaic Acid, Barbituric Acid, Benzilic Acid, Cinnamic Acid,Fumaric Acid, Glutaric Acid, Gluconic Acid, Hexanoic Acid, Lactic Acid,Malic Acid, Oleic Acid, Folic Acid, Propiolic Acid, Propionic Acid,Stearic Acid, Tannic Acid, Trifluoroacetic Acid, Uric Acid, AscorbicAcid, Gallic Acid, and Acetic Acid. The foamed acid, or other acidpresent in the drilling fluid system may also act as an inhibitor orfunction in combination with the acid.

Inhibitors include amines, hydrazines, including hexamine,phenylenediamine, and dimethylethanolamine; sulfite, ascorbic acid,benzotriazole, zinc dithiophosphates, zinc phosphate, tannic acid, zincsalts of organonitrogens, benzalkonium chloride.

In another embodiment the silicate composition includes a sealingmaterial, e.g., a silicate composition, including but not limited tosodium silicate, cesium silicate, potassium silicate, lithium silicate,and rubidium silicate. The sealing material functions by interactingwith an acid to form a dense precipitate or highly viscous material.Preferably the silicate composition is sodium silicate. The silicatecomposition has a density in the range of 2.0-3.5 g/cm³, 2.1-3.0 g/cm³,or 2.5-2.9 g/cm³. Preferably the silicate composition has a density of2.7 g/cm³. The silicate composition is added to the drilling fluidsystem in an amount to effective to form a seal on the face of a wellbore and thereby produce the pressure necessary to carry out drillingoperations, pre- or post-production. The silicate composition may bepresent in the drilling fluid system in an amount by weight based on thetotal weight of the drilling system in the range of 1-50%, 2-40%, or3-30%. Preferably the silicate composition is added in the range of5-15%.

The present invention includes a drilling fluid system using a retardedHCl acid system that contains a diesel (emulsified acid) or gelled acid(viscoelastic (VES) surfactant based or polymer based). The weightingmaterials added to the drilling fluid system includes the sodiumsilicate that to give an effective drilling fluid weight and to preventthe invasion of the mud filtrate into the formation. Comparable to theconventional weighting material Calcium Carbonate (e.g. density=2.7) thelow density of the silicate composition (e.g. density=2.7) can becompensated by using sodium formate as an aqueous phase of the drillingfluid, and/or by adding a little bit from the solution. Cesium,potassium, or sodium formate can also be used for this purpose.

The drilling fluid system dissolves generated cuttings downhole therebyreducing and/or eliminating the need to raise cuttings to the surface.The drilling fluid system can be used to drill the target hydrocarbonproducing formation with zero-invasion with enhanced and controlledfluid loss.

The drilling fluid system includes an aqueous acid solution, a silicate,and a hydrocarbon-based isolation fluid, polymer, or VES. The aqueousacid solution, silicate and hydrocarbon-based isolation fluid form anemulsion such that the aqueous acid solution and silicate aresubstantially delayed from interacting with each other to form a geluntil the emulsion is broken. The emulsion is broken by contact with therock of a hydrocarbon producing formation, e.g., the face of a wellbore. The breaking of the emulsion initiates the interaction between theaqueous acid solution and the silicate such that a gel is formed. Thegel functions to seal the formations at the face of the well bore andcreate a tight impermeable filter cake layer. The impermeable layer doesnot penetrate inside the formation. This allows for control of fluidloss and completely prevents mud filtrate invasion into the formation.This impermeable layer can be removed later as described below. In turn,no stimulation process is required after drilling the formation withsuch drilling fluid system.

Different types of additives can be used in the new drilling fluidsystem, especially for carbonate reservoirs. These additives includecorrosion inhibitors, polymers, surfactants, and emulsifiers.

The method of using the drilling fluid system also controls theformation pressure and cleaning of the well bore. Therefor thepercentage of sodium silicate used in this drilling fluid system, asweighting material to produce the required pressure with a percentagerange of 5% to 15%, will depend on the depth (TVD—total vertical depth)of the target hydrocarbon formation drilling for the formation with thesame permeability. In case of the permeability variation, 5% silicate isadequate for a permeability range of 1 md to 100 md (millidarcy),whereas 100 md to 300 md may require 10% of silicate to generate aneffective filter cake and 15% is desired for higher range ofpermeabilities (from 300 md to 500 md). This is due to the fact that theincrease in permeability requires an extra amount of silicate in orderto be able to produce an effective barrier over the face of the targethydrocarbon formation.

In accordance with another embodiment of the disclosure, the mineralogyof the drilled formation is a significant factor involved in determiningthe proportion of the acid in the drilling fluid system. In particular,there is provided a two mineral composition (dolomite and calcite), inaccordance with an embodiment of the disclosure, for use in determiningthe acid proportion present in a target production zone. Acid in anamount of about 15% by weight can be used in the this drilling fluidsystem if the target drilled formation is calcite to be drilled in lesstime. In the case of dolomite the acid concentration should be raised toachieve the same drilling rate as pure calcite because dolomite haslower reaction rate with the acid compared to calcite. The acidconcentration should be determined earlier based on the reservoirsection mineralogy (% calcite and % dolomite).

API static filtration tests were used to indicate filter cake qualityand filtration volume loss for a drilling fluid system using acidemulsion fluid under specific testing conditions. The tests show theability of the acid emulsion drilling fluid system to form an effectivethin and impermeable filter cake layer and to sustain high differentialpressure without invading through the core and to overcome pressureexerted during pumping the drilling fluids. The static loss test iscarried out under high pressure of 1 and 1500 psi. The tests wereperformed using 500 ml HPHT cell, FIG. 1.

FIG. 1 is an illustration of an assembled high pressure high temperaturefiltration cell. A heating jacket 1-1 allows the filtration cell to staywarm and keeps the filtration cell at an appropriate temperature.Drilling cuttings 1-2 and a drilling fluid 1-9 help to form a filterlayer cake 1-3. A filter media 1-4 is formed underneath the filter layercake 1-3. Compressed air 1-6 enters the system and a flow of air 1-10enters the filtration cell to help form the filter layer cake 1-3. Thecompressed air 1-6 is measured by a pressure gauge 1-5 so that aneffective amount of compressed air enters the filtration cell. Afiltration apparatus 1-7 is located from the filter media 1-4 and adigital balance 1-8 measures the amount of filtered product.

FIG. 2 is a graph that determines the acid amount weight percentagebased on the mineralogy of the drilled formation.

FIG. 3 shows the determination of the adequate quantity of silicateweight percentage to generate an effective filter cake over the face ofthe permeable formation based on its permeability range.

Indiana limestone rock samples were used as filtration medium in thetest to simulate the field drilling operation. The rock sample diameterwas 2.5 inch and the thickness was 0.25 inch with and averagepermeability valid from 1 md to 500 md.

To consider the effect of the drilling cuttings that are, if notproperly removed with solid control equipment, mixing with the drillingfluid during circulation the drilling fluid; 15 to 10% weight percentageof the small drilling cuttings of Indiana limestone rock were added tothe cell of the test to match the real well bore condition.

The various compositions of the described drilling fluid system are thenplaced above the upper face of the core sample in the HPHT cell andpressure was applied by nitrogen above the composition.

It was a demonstrated that the filter cake formed over the upper face ofthe core sample almost has about 1 mml thickness and sustains highdifferential pressure with zero infiltration volume. The formed filtercake also can be destructed by using mixture of HCl and mutual solvent.

Thus, the foregoing discussion discloses and describes merely exemplaryembodiments of the present invention. As will be understood by thoseskilled in the art, the present invention may be embodied in otherspecific forms without departing from the spirit or essentialcharacteristics thereof. Accordingly, the disclosure of the presentinvention is intended to be illustrative, but not limiting of the scopeof the invention, as well as other claims. The disclosure, including anyreadily discernible variants of the teachings herein, define, in part,the scope of the foregoing claim terminology such that no inventivesubject matter is dedicated to the public.

1: An acidic drilling fluid system comprising: an aqueous acidicsolution; a silicate; and a hydrocarbon-based isolation fluid; whereinthe aqueous acidic solution, the silicate and the hydrocarbon-basedisolation fluid are on the form of an emulsion. 2: The acidic drillingfluid system of claim 1, wherein the emulsion breaks by contact with ahydrocarbon producing formation; and upon breaking initiatinginteraction between the aqueous acidic solution and the silicate to forma gel; and form an impermeable filter cake layer to seal the face of thehydrocarbon producing formation. 3: The acidic drilling fluid system ofclaim 1, wherein the viscoelastic surfactant comprises: an aqueousmedium; an inorganic water soluble salt; at least one surfactantselected from the group consisting of an anionic surfactant, a nonionicsurfactant, and a hydrotropic surfactant; and one or more hydrophobicorganic alcohols. 4: The acidic drilling fluid system of claim 3,wherein the anionic surfactant is at least one selected from the groupconsisting of an alkyl sulfate, an alkyl ether sulfate, an alkyl estersulfonate, an alpha olefin sulfonate, a linear alkyl benzene sulfonate,a branched alkyl benzene sulfonate, a linear dodecylbenzene sulfonate, abranched dodecylbenzene sulfonate, an alkyl benzene sulfonic acid, adodecylbenzene sulfonic acid, a sulfosuccinate, a sulfated alcohol, aethoxylated sulfated alcohol, an alcohol sulfonate, an ethoxylated andpropoxylated alcohol sulfonate, an alcohol ether sulfate, an ethoxylatedalcohol ether sulfate, a propoxylated alcohol sulfonate, a sulfatednonyl phenol, an ethoxylated and propoxylated sulfated nonyl phenol, asulfated octyl phenol, an ethoxylated and propoxylated sulfated octylphenol, a sulfated dodecyl phenol, and an ethoxylated and propoxylatedsulfated dodecyl phenol; the nonionic surfactant is selected from thegroup consisting of an ethoxylated octyl phenol, a polypropylene glycol,an ethoxylated linear alcohol, and an ethoxylated nonyl phenol; thehydrotropic surfactant is selected from the group consisting ofdicarboxylic acids, phosphate esters, sodium xylene sulfonate, andsodium dodecyl diphenyl ether disulfonate; and the hydrophobic organicalcohol is selected from the group consisting of ethanol, diethanol,ethylbenzyl alcohol, 2-propanol, 2-ethyl-1-hexanol, 1-octanol, and2-octanol, and mixtures thereof. 5: The acidic drilling fluid system ofclaim 1, wherein the aqueous acidic solution comprises: an aqueous basedfluid; an inert gas; and a blend of at least one alkyltrimethylammmoniumchloride and an amine oxide selected from the group consisting ofbis(2-hydroxyetyl) cocoamine oxide, dimethylhexadecylamine oxide, anddimethyl-hydrogenated tallowamine oxide. 6: The acidic drilling fluidsystem of claim 4, wherein the aqueous based fluid is brine. 7: Theacidic drilling fluid system of claim 1, wherein the aqueous acidicsolution is a gelled acid comprising HCl; and the hydrocarbon-basedisolation fluid is an emulsified diesel fluid. 8: The acidic drillingfluid system of claim 1, wherein the aqueous acidic solution and thesilicate are present in opposite phases of an emulsion and are delayedfrom interacting with one another until the emulsion is broken; andwherein the silicate and the aqueous acidic solution form a gel. 9: Theacidic drilling fluid system of claim 1, wherein the silicate is sodiumsilicate nanoparticles. 10: The acidic drilling fluid system of claim 1,wherein the aqueous acidic solution HCl acid system comprises anemulsified acid or a gelled acid. 11: The acidic drilling fluid systemof claim 10, wherein the emulsified acid is diesel and the gelled acidis a viscoelastic surfactant and/or a polymer. 12: A method of treatinga well present in a hydrocarbon producing formation, comprising:contacting a face of the well with a drilling fluid system comprising:an aqueous acidic solution; a silicate; and a hydrocarbon-basedisolation fluid; wherein the aqueous acidic solution, the silicate andthe hydrocarbon-based isolation fluid are in the form of an emulsion;wherein the emulsion breaks when contacted with the hydrocarbonproducing formation to initiate interaction of the aqueous acidicsolution and the silicate to form a gel and thereby form an impermeablefilter cake layer on the face of the well in the hydrocarbon producingformation. 13: The method of claim 12, wherein the aqueous acidicsolution is a gelled acid comprising HCl; and the hydrocarbon-basedisolation fluid is an emulsified diesel fluid. 14: The method of claim12, further comprising delaying interaction of the aqueous acidicsolution and the silicate until the emulsion is broken. 15: The methodof claim 12, wherein the filter cake layer is formed in an amounteffective to overcome exerted pressure during pumping of the drillingfluid system. 16: The method of claim 12, wherein the emulsified acid isdiesel and the gelled acid is a viscoelastic surfactant based or polymerbased.